Linkage mechanism

ABSTRACT

A linkage mechanism for mounting a movable support to a fixed member for movement between a first position and a second position. The mechanism includes a first linkage arm respectively connected at each end to the fixed member and the movable support and second linkage arm having one end connected to the movable support and the other to a connector located intermediate the ends of the first linkage arm. A third linkage arm extends between the movable support and the connector. The connector controls the movable support during the movement between the first and second positions. A two link arrangement is also disclosed having a pair of linkage arms extending between a movable support and a fixed member. The linkage arms being linked by a connector intermediate their respective ends.

FIELD OF THE INVENTION

[0001] The present invention relates to a linkage mechanism and in particular to a linkage mechanism for mounting a movable support to a fixed support for movement between a first raised position and a second lowered position.

[0002] The invention has been developed primarily for adjustably mounting a keyboard support platform to a desk and will be described hereinafter with reference to that application. However, the invention is not limited to that particular field of use. The mechanism could equally be used in a variety of applications requiring a movable support adjustable relative to a fixed member, for example, a support for a VDU, television monitor or surveillance camera.

BACKGROUND TO THE INVENTION

[0003] In general, a workstation or other desk includes a fixed platform for supporting the variety of tools, books, stationery and other implements utilised by a user of the workstation to achieve the task at hand. In circumstances where use is made of a computer it is desirable to ensure that the user's posture is favourably maintained to protect against unnecessary physical strains and the development of long-term medical conditions as a result of those strains. This is particularly important for those users who have to spend long periods operating the computer on a regular basis.

[0004] To this end, it is known to provide a height adjustable support for a keyboard that is utilised by the user to operate the computer. To achieve the height adjustment, the keyboard support is connected to the fixed platform by a linkage mechanism. In essence, the more common prior art linkage mechanisms comprise a pantographic or parallelogram linkage that allows some degree of height adjustment of the keyboard support. The pantographic linkage maintains the keyboard support substantially parallel to the platform throughout the movement, while the parallelogram linkage results in some tilting of the keyboard support during that same movement.

[0005] Examples of such known linkages are described in U.S. Pat. No. 4,616,798 (Smeenge), U.S. Pat. No. 5,037, 054 (McConnell), U.S. Pat. No. 5,292,097 (Russell) and) U.S. Pat. No. 5,707,034 (Cotterill).

[0006] For the prior art linkages to provide the necessary strength for the desired application, there must be sufficient vertical distance between the arms that comprise the pantograph or parallelogram. This results in a bulky arrangement that extends downwardly from the underside of the platform and the keyboard support. Accordingly, while height adjustment of the keyboard is achieved, an additional hazard is created in that the user is increasingly likely to inadvertently contact the linkage mechanism with their legs. This can be painful and injurious and is particularly undesirable. This problem is exacerbated due to the sharp edges that are often included in prior art linkage application. These prior art arrangements are also subject to support instability and reduced options for design flexibility. It will be appreciated that any reduction in the bulkiness of the linkage provides advantages in a variety of other applications to which such linkages may be applied.

SUMMARY OF THE INVENTION

[0007] It is an object of the present invention to overcome or ameliorate at least one of the disadvantages of the prior art, or to provide a useful alternative.

[0008] According to a first aspect of the invention there is provided a linkage mechanism for mounting a movable support to a fixed member for movement between a first position and a second position, the mechanism including:

[0009] a first linkage arm that extends between a first end and a second end that are respectively connected to the fixed member and the movable support;

[0010] a second linkage arm that extends between a third end and a fourth end, wherein the third end is connected to the fixed support;

[0011] a third linkage arm that extends between a fifth end and a sixth end, wherein the sixth end is connected to the movable support; and

[0012] a connector for connecting the fourth end and the fifth end to the first linkage arm intermediate the first end and the second end for controlling the movable support during the movement between the first and second positions.

[0013] Preferably, the connector also controls the attitude of the movable support during the movement of between the first and second positions.

[0014] Preferably also, the first arm includes a control formation and the connector slideably connects the fourth end and the fifth end to the control formation. More preferably, the control formation is a slot in the first linkage arm and the connector is a pin that connects the fourth and the fifth ends and which is slideably received in the slot. In other embodiments, the connector is a fourth linkage that extends between a seventh end and an eighth end that are respectively connected to the fourth end and the fifth end by respective pins, wherein the control formation includes two slots that are spaced apart in the first linkage arm and which receive respective one of the pins. In further embodiments the two slots are joined to form a single slot.

[0015] In a preferred form, the first, second, third and sixth ends are pivotally connected to the respective fixed member and movable support. More preferably, the first, second, third and sixth ends are pivotally fixed or attached to the respective fixed member and movable support. That is, the ends are connected for pivotal movement only. In other embodiments one of the first, second, third and sixth ends are pivotally and slideably connected to the respective fixed member and movable support. More preferably, the pivotal and slideable connection allows selective locking of the support against relative movement. Even more preferably, the pivotal and slideable connection allows selective locking at one of a plurality of discrete further positions between the first and second positions.

[0016] According to a second aspect of the invention there is provided a movable support for a load, the movable support being mounted to a fixed support by a linkage mechanism for movement between a raised position and a lowered position, the support including:

[0017] a platform having an upper surface for supporting the load, the upper surface extending substantially along a plane; and

[0018] a mount extending upwardly from the platform for engaging with the linkage mechanism at an upper mounting point and a lower mounting point that is spaced apart from the upper mounting point, the mounting points being on opposite sides of the plane.

[0019] Preferably, the lower mounting point is immediately adjacent to the plane. In other embodiments the mounting points are equally spaced from the plane.

[0020] Preferably also, the mount extends below the platform for providing additional load bearing capacity. More preferably, the mount includes two spaced apart support formations that each extend from one end that is connected to the linkage mechanism to another end that is disposed beneath the platform. Even more preferably, the support formations are mechanically linked by a cross member.

[0021] In a preferred form, the platform includes a front edge, a rear edge spaced apart from the front edge, and two side edges joining the front edge and the rear edge. More preferably, the mount extends normally from the platform and defines the front edge. Even more preferably, the rear edge is bevelled or otherwise rounded to reduce the risk of inadvertent contact with the rear edge causing injury to a user of the support.

[0022] Preferably, the linkage mechanism includes a lock for selectively preventing and allowing the movement between the raised and the lowered positions.

[0023] According to a third aspect of the invention there is provided an adjustable support for a load, the adjustable support being mountable to a fixed support by a linkage and including:

[0024] a base extending from the linkage and providing two spaced apart guide formations;

[0025] a platform for supporting the load, wherein the platform is mounted to the base for movement between a first position and a second position; and

[0026] two spaced apart control formations being associated with the platform for respectively inter-engaging with the guide formations such that the movement of the platform between the first position and the second position results in a change of inclination of the platform with respect to the base.

[0027] Preferably, guide formations are respective slots formed in the base and the control formations are respective sliders that extend from the platform and which are received within the corresponding slots. More preferably, the platform includes a platen having a substantially planar upper surface upon which the load is supported and a lower surface to which the sliders are mounted.

[0028] Preferably also, the guide formations are inclined with respect to each other to allow the application of an automatic locking force to lock the platform at one of a plurality of positions intermediate the first and the second positions. More preferably, the locking force is increased with the weight of the load.

[0029] In a preferred form, the platform, during movement between the first and second positions, follows a predetermined path due to the inter-engagement between the guide formations and the control formations. More preferably, the predetermined path includes both transverse and rotational components.

[0030] According to a fourth aspect of the invention there is provided an adjustable support for a load, the adjustable support being mountable to a fixed support and including:

[0031] a base for mounting to fixed support and having two spaced apart guide formations;

[0032] a platform for supporting the load, wherein the platform is mounted to the base for movement between a first position and a second position; and

[0033] two spaced apart control formations being associated with the platform for respectively inter-engaging with the guide formations such that the movement of the platform between the first position and the second position results in a change of inclination of the platform with respect to the base.

[0034] Preferably, the guide formations are slots and the control formation are sliders that are received within the respective slots, wherein the slots are inclined with respect to each other so that the platform is gravitationally biased into locking engagement with the base. More preferably, the locking engagement is overcome by a force that is applied by a user such that, upon the removal of that force the platform returns into locking engagement with the base.

[0035] According to a fifth aspect of the invention there is provided a linkage mechanism for mounting a movable support to a fixed member for movement between a first position and a second position, the mechanism including:

[0036] an arm that extends between a first end and a second end that are respectively connected to the fixed member and the movable support;

[0037] a linkage that extends between a third end and a fourth end that are respectively connected to the fixed member and the movable support, the linkage also being connected, intermediate the third end and the fourth end, to the arm intermediate the first end and the second end for controlling the attitude of the movable support during the movement between the first and second positions.

[0038] Preferably, the movement of the movable support between the first and second positions is along a predetermined path. More preferably, the attitude of the movable platform remains substantially constant throughout the movement between the first and the second positions.

[0039] Preferably also, the linkage includes a first linkage member and a second linkage member that are respectively connected to the fixed and the movable support, the members being rotatably mounted to each other at a mounting point. More preferably, the mounting point corresponds to the connection between the arm and the linkage.

[0040] In other embodiments, the linkage includes a first, second and third linkage members, where the first and the second members are respectively connected to the fixed and the movable support and the third element extends between and is connected to the first and the second members.

[0041] Preferably, the arm includes a guide formation intermediate the first and second ends and the linkage includes a control formation intermediate the third and fourth ends wherein the guide and control formations define the connection between the arm and the linkage. More preferably, the control formation is mounted for relative movement with respect to the guide formation during the movement of the movable support between the first and the second positions. Even more preferably, the guide formation is a slot formed in the arm and the control formation is a slider that extends from the linkage and which is received in the slot for slideable progression along the slot during the movement of the movable support between the first and the second positions. Preferably, the slot has two ends that are abutted by the slider when the movable support is in the first and second positions respectively.

[0042] Preferably also, the linkage mechanism includes a lock for selectively preventing and allowing the movement between the first and second positions.

[0043] According to a sixth aspect of the invention there is provided a linkage mechanism for mounting a movable support to a fixed member for movement between a first position and a second position, the mechanism including:

[0044] a first linkage that extends longitudinally between a first end and a second end that are respectively connected to the fixed member and the movable support;

[0045] a second linkage arm that extends longitudinally between a third end and a fourth end that are respectively connected to the fixed member and the movable support;

[0046] a first connection element disposed intermediate the first end and the second end; and

[0047] a second connection element disposed intermediate the third and the fourth end and being mechanically linked with the first connection element during movement between the first and second positions for ensuring that a transverse load applied to any one of the arms is shared by both arms.

[0048] Preferably also, the first connection element includes a slot in the first arm and the second connection element includes a pin that travels along the slot during the movement between the first and second positions. More preferably, the second linkage arm includes a first link that extends between the third end and a fifth end and a second link that extends between the fourth end and the 5 fifth end. Even more preferably, the pin extends from the fifth end.

[0049] Further embodiments and exemplifications of the invention will become apparent from the following detailed description.

BRIEF DESCRIPTION OF DRAWINGS

[0050] Preferred embodiments of the various aspects of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0051]FIG. 1 shows a side elevation view of one embodiment of the present invention;

[0052]FIG. 2 shows a side elevation view of a second embodiment of the present invention;

[0053]FIG. 3 shows a side elevation view of a third embodiment of the present invention;

[0054]FIG. 4 shows a side elevation view of a fourth embodiment of the present invention;

[0055]FIG. 5 shows an enlarged side elevation view of the platen arrangement of FIG. 4;

[0056]FIG. 6 shows a side elevation view of fifth embodiment of the present invention;

[0057]FIG. 7 shows a side elevation view of one embodiment of the present invention with the linkage in a first position;

[0058]FIG. 8 shows the embodiment of FIG. 7 with the linkage in a second position;

[0059]FIG. 9 shows an enlarged side elevation view of the movable support of FIG. 7;

[0060]FIG. 10 shows a side elevation of a further embodiment of the present invention;

[0061]FIGS. 11A and 11B show a side view of the locking key of FIG. 10 in an unlocked and locked position, respectively;

[0062]FIGS. 12A and 12B show a plan view of the locking key of FIG. 10 in an unlocked and locked position, respectively, with the slot path shown in dotted outline;

[0063]FIG. 13 shows a side elevation of a further embodiment of the first aspect of the invention; and

[0064]FIG. 14 shows a side elevation of a further embodiment of the present invention; and

[0065]FIG. 15 shows a plan view of the embodiment of FIG. 14.

DETAILED DESCRIPTION OF THE INVENTION

[0066] Referring to the drawings, the various preferred embodiments of the invention will now be described. The same numbering will be used to indicate the same or similar features of each of the embodiments.

[0067]FIG. 1 shows a linkage mechanism 5 arranged between a fixed member 6 and a movable support 7. The linkage mechanism 5 in this embodiment comprises a first bowed linkage arm 8 pivotally attached at one end 9 to a bracket 10 fixed to the member 6 and pivotally attached at a second end 11 to the movable support 7. A second linkage arm 12 is pivotally attached at one end 13 to the bracket 10 at a connection point 14 which is spaced from and above the connection point 15 of the first linkage arm 8 and at its other end 16 to a connector pin 17. A third linkage arm 18 is pivotally attached at one end 19 to the movable support 7 at a connection point 20 spaced from and above the connection point 21 of the first linkage arm 8 and at its other end 22 to the connector pin 17. The connector pin 17 links the respective ends 16 and 22 of the second and third linkage arms to a point 23 intermediate the ends of the first linkage arm 8. Connector pin 17 passes through the ends 16 and 22 and is slideably received in a slot 24. The movable support may be raised and lowered between a first and second position defined by the limits of movement of connector pin 17 within slot 24.

[0068] Each of the pivotal attachments described can be considered fixed in they typically consist of a fixed pin or bush mating with a complementary hole to provide pivotal movement about a fixed axis of the pin. In alternative embodiments, the attachment points may be provided by a movable pivot, typically a pin or bush slideably mating with a slot though other functionally equivalent mechanisms could be used.

[0069]FIG. 2 shows a second embodiment of the first aspect of the present invention. The linkage mechanism 5 in this embodiment comprises a first linkage arm 8 pivotally attached at one end 9 to a bracket 10 fixed to the member 6 and pivotally attached at a second end 11 to the movable support 7. A second linkage arm 12 is pivotally attached at one end 13 to the bracket 10 at a connection point 14 which is spaced from and above the connection point 15 of the first linkage arm 8 and at its other end 16 to a connector pin 17. A third linkage arm 18 is pivotally attached at one end 19 to the movable support 7 at a connection point 20 spaced from and above the connection point 21 of the first linkage arm 8 and at its other end 22 to a connection point 30 intermediate the ends of the second linkage arm 12. The connector pin 17 links the respective ends 16 and 22 of the second and third linkage arms to a point 23 intermediate the ends of the first linkage arm 8. Connector pin 17 passes through the ends 16 and 22 and is slideably received in a slot 24.

[0070]FIG. 3 shows an embodiment of the second aspect of the invention. The Figure illustrates the first and second positions of the movable support 7 and the corresponding movement of the linkage mechanism 5. The linkage mechanism 5 in this embodiment comprises a first linkage arm 8 which is reverse-bowed about a central point and pivotally attached at one end 9 to a bracket 10 and pivotally attached at a second end 11 to the movable support 7. A second linkage arm 12 is pivotally attached at one end 13 to the bracket 10 at a connection point 14 which is spaced from and above and in front of the connection point 15 of the first linkage arm 8 and at its other end 16 to a connector pin 17. A third linkage arm 18 is pivotally attached at one end 19 to the movable support 7 at a connection point 20 spaced from and above the connection point 21 of the first linkage arm 8 and at its other end 22 to the connector pin 17. The connector pin 17 links the respective ends 16 and 22 of the second and third linkage arms to a point 23 intermediate the ends of the first linkage arm 8. Connector pin 17 passes through the ends 16 and 22 and is slideably received in a slot 24. In this embodiment the movable support 7 includes a platform or surface 35 for supporting a load. Again, as shown in the figures the movable support 7 may be raised and lowered between a first and second position defined by the limits of movement of connector pin 17 within slot 24.

[0071]FIGS. 4 and 5 illustrate the third aspect of the invention and are shown employing a linkage 5 according to the second aspect though it will appreciated other forms of linkage may be used. Referring in particular to FIG. 6, the is movable support 7 is generally L-shaped to provide a support platform 35. A pair of spaced guide formations in the form of slots 36 and 37 are provided respectively adjacent the apex 38 of the platform 35 and the distal end 39 of the support platform 35. An adjustable platen 40 having a pair of arms 41 and 42 each of which are provided with a respective control formation 43 and 44 extending normal to the longitudinal axis of the arms. The control formations 43 and 44 are in the form of bushes or pins receivable in an associated guide slot 36 and 37. The slots and arms are configured relative to one another such that movement of the control formations between the extremities of their associated slots results in movement of the platen 40 between a first and second position, the change in position further resulting in a change of inclination of the platen 40 as illustrated in dotted outline in FIG. 6. The inclination of the guide slots 36 and 37 relative to each other provides for an automatic locking force to be applied to the platen 40 when located at positions intermediate the first and second positions.

[0072]FIG. 6 illustrates an embodiment of a fourth aspect of the present invention. The embodiment is similar to that of FIG. 5 but does not require the linkage and uses a fixed support bracket 35′ in the form of the support platform 35. The control of the platen 40 operates in a similar manner and the slots 36 and 37 are inclined relative to each other so that the platen is gravitationally biased into locking engagement with the base bracket 35′. Translational movement of the platen 40 under a force applied by the user can move it to a second position as illustrated in dotted outline. Once the force is removed the platen 40 will return to the locked position.

[0073] FIGS. 7 to 9 illustrate a further embodiment of the present invention. The 5 linkage mechanism 5 in this embodiment comprises a first bowed linkage arm 8 pivotally attached at one end 9 to a bracket 10 and pivotally attached at its other end 11 to the movable support 7. A second bowed linkage arm 12 is pivotally attached at one end 13 to the bracket 10 at a connection point 14 which is spaced from and above the connection point 15 of the first linkage arm 8 and at its other end 16 to the movable support 7 at an attachment point 20. The first linkage arm 8 is pivotally attached at its end 11 to an attachment point 45 which is in the form of a slot 46 which slideably receives a bush or pin 47 to provide a movable pivotable attachment. Attachment point 45 is spaced from and below the connection point 20 of the second linkage arm. The second linkage arm 12 is provided with a slot 24 for slideably receiving a connector pin 17 extending normally from the first linkage arm 8 so as to maintain, in conjunction with movable pivot 45, a constant attitude of the movable support.

[0074]FIGS. 10, 11A, 11B, 12A and 12B illustrate a further embodiment of the present invention and in particular a locking mechanism for the linkage mechanism. The linkage mechanism 5 in this embodiment comprises a first bowed linkage arm 8 pivotally attached at one end 9 to a bracket 10 fixed to the member 6 and pivotally attached at a second end 11 to the movable support 7. A second linkage arm 12 is pivotally attached at one end 13 to the bracket 10 at a connection point 14 which is spaced from and below the connection point 15 of the first linkage arm 8 and at its other end 16 to a connector pin 17. A third linkage arm 18 is pivotally attached at one end 19 to the movable support 7 at a connection point 20 spaced from and below the connection point 21 of the first linkage arm 8 and at its other end 22 to the connector pin 17. The connector pin 17 links the respective ends 16 and 22 of the second and third linkage arms to a point 23 intermediate the ends of the first linkage arm 8. Connector pin 17 passes through the ends 16 and 22 and is slideably received in a slot 24.

[0075] The pivotal attachment at end 9 of the linkage arm 8 is a movable pivot comprising a horizontal slot 50 in the end 9 slideably receiving a pin or bush 49 extending from the bracket 10. This enables translational to and fro movement of the movable support 7 and associated linkage 5 relative to the bracket 10 and fixed member 6. The translational movement being between a locked position and an unlocked position.

[0076] The bracket 10 is provided with an arcuate slot 51 slideably receiving a locking key 52 which is pivotally attached to linkage arm 8. The locking key 52 shown in detail in FIG. 11 has a tapered groove 53 in one side 54 which slideably receives one edge 55 of the slot 51. In said unlocked position the locking key 52 slides freely along the slot edge 55, however, when linkage is moved horizontally by the user to a locked position, the key groove engages with the edge of the slot 55 to lock the linkage mechanism in any desired position between the normal extremities of movement set by slot 24.

[0077] A further embodiment of the first aspect of the invention is illustrated in FIG. 13. The linkage mechanism 60 in this embodiment comprises a first linkage arm 8 pivotally attached at one end 9 to a bracket 10 fixed to the member 6. A second linkage arm 12 is pivotally attached at one end 13 to the bracket 10 at a connection point 14 which is spaced from and above the connection point 15 of the first linkage arm 8 and at its other end 16 to a connector pin 17. A third linkage arm 18 is pivotally attached at one end 19 to the movable support 7 at a connection point 20 and at its other end 22 to a fourth linkage arm 61 at one end 62. A further connector pin 63 is provided at the other end 64 of the fourth linkage arm 61.

[0078] The other end 11 of first linkage arm 8 is pivotally attached to one end 65 of a first link 66 . The other end 67 of the first link 66 is provided with a connector pin 68 which pivotally connects to one end 69 of a second link 70 and is slideably received in a slot 71 provided intermediate the ends 19 and 22 of the third linkage arm 18. The other end 72 of the second link 70 is pivotally attached to the movable support 7 at a connection point 21 spaced from and below connection point 20. A third link 76 connects the pivotal connection point 77 of third and fourth linkage arms 18, 61 and the pivotal connection point 78 of the first linkage arm 8 and the first link 66.

[0079] The connector pin 17 links end 16 of the second linkage arm to a point 23 intermediate the ends of the first linkage arm 8. Connector pin 17 passes through the end 16 and is slideably received in a slot 24 formed in linkage arm. The connector pin 63 links end 64 of of the fourth linkage arm to a point 73 spaced from and adjacent point 23. Connector pin 63 passes through the end 64 and is slideably received in a slot 74 formed in linkage arm. 8. Slots 24 and 74 may be constituted by a single slot. In this example, the movable support 7 is shown supporting a VDU 75.

[0080]FIGS. 14 and 15 illustrate an embodiment of the invention where the disposition of the various linkage arms relative to one another serve to provide torsional rigidity to the linkage mechanism.

[0081] The linkage mechanism 5 in this embodiment comprises a first bowed linkage arm 8 pivotally attached at one end 9 to a bracket 10 fixed to the member 6 and pivotally attached at a second end 11 to the movable support 7. A second linkage arm 12 is pivotally attached at one end 13 to the bracket 10 at a connection point 14 which is spaced from and above the connection point 15 of the first linkage arm 8 and at its other end 16 to a connector pin 17. A third linkage arm 18 is pivotally attached at one end 19 to the movable support 7 at a connection point 20 spaced from and above the connection point 21 of the first linkage arm 8 and at its other end 22 to the connector pin 17. The connector pin 17 links the respective ends 16 and 22 of the second and third linkage arms which are located on opposite sides of the linkage arm 8 to a point 23 intermediate the ends of the first linkage arm 8. Connector pin 17 passes through the end 16, slot 24 and then end 22. Linkage arm 8 is effectively sandwiched between arms 12 and 18.

[0082] The sandwich arrangement of the various arms provides for uniform distribution of the load and resists torsional and compressive forces applied to the linkage mechanism.

[0083] It will be appreciated that further embodiments and exemplifications of the invention are possible without departing from the spirit or scope of the invention described. 

I claim:
 1. A linkage mechanism for mounting a movable support to a fixed member for movement between a first position and a second position, the mechanism including: a first linkage arm that extends between a first end and a second end that are respectively connected to the fixed member and the movable support; a second linkage arm that extends between a third end and a fourth end, wherein the third end is connected to the fixed member; a third linkage arm that extends between a fifth end and a sixth end, wherein the sixth end is connected to the movable support; and a connector for connecting the fourth end and the fifth end to the first linkage arm intermediate the first end and the second end for controlling the movable support during the movement between the first and second positions.
 2. A linkage mechanism according to claim 1 wherein the connector further controls the attitude of the movable support during the movement of between the first and second positions.
 3. A linkage mechanism according to claim 1 wherein the first linkage arm includes a control formation and wherein the connector slideably connects the fourth end and the fifth end to the control formation.
 4. A linkage mechanism according to claim 3 wherein the control formation is a slot in the first arm and the connector is a pin that connects the fourth and the fifth ends and which is slideably received in the slot.
 5. A linkage mechanism according to claim 1 wherein the connector is a fourth linkage arm that extends between a seventh end and an eighth end that are respectively connected to the fourth end and the fifth end by respective pins, and wherein the control formation includes two slots that are spaced apart in the first linkage arm and which receive respective one of the pins.
 6. A linkage mechanism according to claim 5 wherein the two slots are joined to form a single slot.
 7. A linkage mechanism according to claim 1 wherein the first, second, third and sixth ends are pivotally connected to the respective fixed member and movable support.
 8. A linkage mechanism according to claim 7 wherein the first, second, third and sixth ends are pivotally attached at a fixed point to the respective fixed member and movable support.
 9. A linkage mechanism according to claim 7 wherein one of the first, second, third and sixth ends are pivotally and slideably connected to the respective fixed member and movable support.
 10. A linkage mechanism according to claim 9 wherein the pivotal and slideable connection allows selective locking of the support against relative movement.
 11. A linkage mechanism according to claim 10 wherein the pivotal and slideable connection allows selective locking at one of a plurality of discrete further positions between the first and second positions.
 12. A movable support for a load, the movable support being mounted to a fixed member by a linkage mechanism for movement between a raised position and a lowered position, the support including: a platform having an upper surface for supporting the load, the upper surface extending substantially along a plane; and a mount extending upwardly from the platform for engaging with the linkage mechanism at an upper mounting point and a lower mounting point that is spaced apart from the upper mounting point, the mounting points being on opposite sides of the plane.
 13. A movable support according to claim 12 wherein the lower mounting point is adjacent to the plane.
 14. A movable support according to claim 12 wherein the mounting points are equally spaced from the plane.
 15. A movable support according to claim 12 wherein the mount extends below the platform for providing additional load bearing capacity.
 16. A movable support according to claim 15 wherein the mount includes two spaced apart support formations that each extend from one end that is connected to the linkage mechanism to another end that is disposed beneath the platform.
 17. A movable support according to claim 16 wherein the support formations are mechanically linked by a cross member.
 18. A movable support according to claim 12 wherein the platform includes a front edge, a rear edge spaced apart from the front edge, and two side edges joining the front edge and the rear edge.
 19. A movable support according to claim 18 wherein the mount extends normally from the platform and defines the front edge.
 20. A movable support according to claim 18 wherein the rear edge is bevelled or otherwise rounded to reduce the risk of inadvertent contact with the rear edge causing injury to a user of the support.
 21. A movable support according to claim 12 wherein the linkage mechanism includes a lock for selectively preventing and allowing the movement between the raised and the lowered positions.
 22. An adjustable support for a load, the adjustable support being mountable to a fixed member by a linkage and including: a base extending from the linkage and providing two spaced apart guide formations; a platform for supporting the load, wherein the platform is mounted to the base for movement between a first position and a second position; and two spaced apart control formations being associated with the platform for respectively inter-engaging with the guide formations such that the movement of the platform between the first position and the second position results in a change of inclination of the platform with respect to the base.
 23. An adjustable support according to claim 22 wherein the guide formations are respective slots formed in the base and the control formations are respective sliders that extend from the platform and which are received within the corresponding slots.
 24. An adjustable support according to claim 22 wherein the platform includes a platen having a substantially planar upper surface upon which the load is supported and a lower surface to which the sliders are mounted.
 25. An adjustable support according to claim 22 wherein the guide formations are inclined with respect to each other to allow the application of an automatic locking force to lock the platform at one of a plurality of further positions intermediate the first and the second positions.
 26. An adjustable support according to claim 25 wherein the locking force is increased with the weight of the load.
 27. An adjustable support according to claim 22 wherein the platform, during movement between the first and second positions, follows a predetermined path due to the inter-engagement between the guide formations and the control formations.
 28. An adjustable support according to claim 27 wherein the predetermined path includes both transverse and rotational components.
 29. An adjustable support for a load, the adjustable support being mountable to a fixed member and including: a base for mounting to fixed member and having two spaced apart guide formations; a platform for supporting the load, wherein the platform is mounted to the base for movement between a first position and a second position; and two spaced apart control formations being associated with the platform for respectively inter-engaging with the guide formations such that the movement of the platform between the first position and the second position results in a change of inclination of the platform with respect to the base.
 30. An adjustable support according to claim 29, wherein the guide formations are slots and the control formation are sliders that are received within the respective slots, and wherein the slots are inclined with respect to each other so that the platform is gravitationally biased into locking engagement with the base.
 31. An adjustable support according to claim 30 wherein the locking engagement is overcome by a force that is applied by a user such that, upon the removal of that force the platform returns into locking engagement with the base.
 32. A linkage mechanism for mounting a movable support to a fixed member for movement between a first position and a second position, the mechanism including: an arm that extends between a first end and a second end that are respectively connected to the fixed member and the movable support; a linkage that extends between a third end and a fourth end that are respectively connected to the fixed member and the movable support, the linkage further being connected, intermediate the third end and the fourth end, to the arm intermediate the first end and the second end for controlling the attitude of the movable support during the movement between the first and second positions.
 33. A linkage mechanism according to claim 32 wherein the movement of the movable support between the first and second positions is along a predetermined path.
 34. A linkage mechanism according to claim 32 wherein the attitude of the movable platform remains substantially constant throughout the movement between the first and second positions.
 35. A linkage mechanism according to claim 32 wherein the linkage includes a first linkage member and a second linkage member that are respectively connected to the fixed member and the movable support, the members being rotatably mounted to each other at a mounting point.
 36. A linkage mechanism according to claim 35 the mounting point corresponds to the connection between the arm and the linkage.
 37. A linkage mechanism according to claim 32 wherein the linkage includes a first, second and third linkage members, where the first and the second linkage members are respectively connected to the fixed member and the movable support and the third linkage member extends between and is connected to the first and the second linkage members.
 38. A linkage mechanism according to claim 32 wherein the arm includes a guide formation intermediate the first and second ends and the linkage includes a control formation intermediate the third and fourth ends wherein the guide and control formations define the connection between the arm and the linkage.
 39. A linkage mechanism according to claim 38 wherein the control formation is mounted for relative movement with respect to the guide formation during the movement of the movable support between the first and second positions.
 40. A linkage mechanism according to claim 39 wherein the guide formation is a slot formed in the arm and the control formation is a slider that extends from the linkage and which is received in the slot for slideable progression along the slot during the movement of the movable support between the first and second positions.
 41. A linkage mechanism according to claim 40 wherein the slot has two ends that are abutted by the slider when the movable support is in the first and second positions respectively.
 42. A linkage mechanism according to claim 32 further including a lock for selectively preventing and allowing the movement between the first and second positions. 43 A linkage mechanism according to claim 42 wherein the lock includes a key element positioned on said arm and selectively engageable with said fixed member to prevent and allow said movement.
 44. A linkage mechanism according to claim 43 wherein said key is operated by translational movement of said movable support relative to said fixed member.
 45. A linkage mechanism according to claim 32 wherein at least one of the connections of the arm or linkage to the respective fixed member or movable support is a pivotal and slideable connection.
 46. A linkage mechanism for mounting a movable support to a fixed member for movement between a first position and a second position, the mechanism including: a first linkage arm that extends longitudinally between a first end and a second end that are respectively connected to the fixed member and the movable support; a second linkage arm that extends longitudinally between a third end and a fourth end that are respectively connected to the fixed member and the movable support; a first connection element disposed intermediate the first end and the second end; and a second connection element disposed intermediate the third and the fourth end and being mechanically linked with the first connection element during movement between the first and second positions for ensuring that a transverse load applied to any one of the arms is shared by both arms.
 47. A linkage mechanism according to claim 46 wherein the first connection element includes a slot in the first linkage arm and the second connection element includes a pin that travels along the slot during the movement between the first and second positions.
 48. A linkage mechanism according to claim 47 wherein the second linkage arm includes a first link that extends between the third end and a fifth end and a second link that extends between the fourth end and the fifth end.
 49. A linkage mechanism according to claim 48 wherein the pin extends from the fifth end. 